1. Field of the Invention
The present invention generally relates to an in vivo surgical instrument and, more particularly, to the surgical instrument suited, but not exclusively limited thereto, for use in ophthalmic surgical operations for the removal of the diseased vitreous or in the treatment of a cataract.
2. Description of the Prior Art
It is well known that in an opthalmic surgical operation for the removal of the diseased vitreous or for the treatment of cataract, a surgical cutting instrument is utilized to remove prolapsed anterior vitreous. According to the state of art, the surgical cutting instrument is available in various types. One exemplary surgical cutting instrument comprises an outer tube having a closed distal end, and an inner tube having a distal end and being axially slidably inserted in the outer tube. The outer tube has a perforation defined therein at a position axially inwardly of the distal end thereof. The inner tube in the outer tube is adapted to be reciprocatingly moved axially within the outer tube. The distal end of the inner tube and a peripheral lip region defining the aperture in the outer tube cooperate with each other to provide a scissor action when the inner tube is axially moved relative to the outer tube to cut an affected tissue. The removed affected tissue is then sucked outwardly through the inner tube under the influence of a sucking force developed in the tube system.
In this known surgical cutting instrument, the cutting of the affected tissue takes place in a direction counter to the direction in which the sucking force acts, that is, in a direction confronting the closed distal end of the outer tube. Accordingly, it is necessary that the aperture defined in the outer tube adjacent the closed distal end be closed by a distal end portion of the inner tube during the stroke of movement of the inner tube.
Considering that the distal end of the outer tube is closed, and that when the inner tube closes the aperture in the outer tube subsequent to the cutting of the affected tissue, the affected tissue removed tends to be pushed into a space delimited between the closed distal end of the outer tube and the distal end of the inner tube to such an extent as to result in an occlusion. Once this occlusion occurs in the tube system, no surgical operation can be carried out without retraumatization.
Also, the cutting of the affected tissue and the suction of the removed tissue are correlated with each other and, therefore, it is desirable that the direction in which the cutting takes place, and the direction in which the removed tissue is sucked for the discharge thereof to be removed from the tube system be identical with each other in order to improve cutting efficiency.
Once the aperture defined in the outer tube adjacent the closed distal end is closed by the inner tube in the manner as hereinabove described, the eventual withdrawal of the tube system of the surgical cutting instrument from the eyeball, or the positional adjustment of the tube system within the eyeball may often result in an undesirable pull of the retina, vascular tissue or the like, by being sandwiched between the outer and inner tubes which may result in retraumatization.
In addition, in order to assure a safe removal of the affected tissue in the eyeball, it is required that the inner and outer tubes fit substantially perfectly into one another being capable of being slid with respect to each other. However, the substantially perfect fit between the outer and inner tubes requires time-consuming and complicated machining processes and assemblage, and therefore, the problem associated with the undesirable pull of sound tissue which is peripheral to the affected tissue, cannot be avoided. Accordingly, a compromise is that one side edge of the peripheral lip region defining the aperture in the outer tube is so shaped as to achieve a scissor action in cooperation with a peripheral edge at the distal end of the inner tube as the latter is moved past the aperture.
Thus, the prior art surgical cutting instrument has an additional problem in that the cutting performance is relatively low enough to substantially reduce a safety factor.
Accordingly, the present invention has been devised to provide an improved and safe surgical cutting instrument which does not cause retraumatization and which is capable of exhibiting a relatively high cutting efficiency for a substantially prolonged period of use.